Author
Topic: Yoke hitch (Read 11889 times)

Do you need a two-wrap hitch which grips an object so tightly, that you can not force it to slide on its surface towards ANY direction ? That you can not even force it to revolve around the axis of a round sleek pole ? Here it is - and I am not aware of any one else. Essentially, it is an "abbreviated" TackleClamp hitch, which has one less wrap - but, what is most important, it can be pre-tensioned by pulling the one, and the one only, end - i.e., it does not require the pulling of both ends, the one after the other, alternately, as most tight hitches do. The ways to "finish" this hitch, and secure the Tail End, are many : we have to attach the Tail End within a bight, at its tip, and this can be achieved by using a variety of knots. In the pictures of the hitch shown in this thread, I had used a slipped overhand knot, entangled into the tip of the bight so that the two legs of its slipped tail are encircled by both Us, the rim of the overhand knot and the rim of the bight. I thought that this was the simplest solution, which, on the one hand is very secure, and, on the other, it retains the TIBness of the hitch. A yet simpler solution is shown at the fourth attached picture. However, a curious knot tyer may find another, even simpler and also very secure solution which I may had missed. There is a strange thing in this hitch : From the moment one starts to pull the end, the hitch and/or the pole rotate around their common axis, and this means two things : In order to exploit the advantage of a direct pull against the pole ( i.e., a pull perpendicularly to the axis and the surface of the pole ), one has either to revolve around the pole, or to make the pole rotate around itself ! On a pole that can not rotate, or that it has not enough room around it to enable the pull of its Standing End from different directions, one may not be able to tension this hitch as much as it takes.

More pictures of this hitch, so one can get a feeling of how simple it is : it does not consume more material than many much less tight hitches. In the first three pictures, I have not included the slipped overhand knot "finish", to facilitate the reading of the knot s structure. When I tied it around a glass tube, I could nt pre-tension it, of course. Tied on this particular rope, of this material and size, it starts to grip and squeeze the glass tube of this particular diameter when the two crossing points of the tackled wraps are at diametrically opposite points, as shown in the pictures. On a less sleek or more thick pole, it may start to grip it even before this point - so one has to take many parameters into account, and even then he may not be able to predict how much, exactly, the two crossing points of the tackled wraps will approach each other at the very end, when the hitch will become as much pre-tensioned as possible. The optimum distance between the two sides of the "yoke" is about 1/4th of the pole s circumference, so the three umbilical cords are almost straight, and the friction forces on them, which impede their pulling, from the surface of the pole is not very strong - but we can seldom achieve this optimum ! So, to avoid the danger to have the two parts "kiss" each other prematurely, before the hitch has been maximally pre-tensioned, I prefer to take the slack of the knot, and start pulling its end, sooner rather than later.

In those pictures, we can see how much the Yoke hitch looks like an "abbreviated" TackleClamp hith. However, tied around a not-so-fragile object, it is easy to make the two-wrap-sections side much more extended than the three-wrap-sections side : this hitch is a two-wrap hitch, and we may see this more easily if we tie it around a thicker pole.

Photos of the Yoke hitch ( taken from slightly different angles ) in its most "extreme" initial position, where the two parts of the tackle "kiss" each other at the "rear" side of the hitch - just before the start of the pre-tensioning. However, if we start from this position, the hitch would probably "close", and become maximally pre-tensioned, too early, before the two parts of the tackle re-approach each other as closely as we want : I reckon that a distance of about 1/2 pole diameter would be the optimum ?

Two pictures of the "loose knot", where all its elements are in the position we would had wished them to be, when the knot will be maximally tightened. We see that the two parts of the tackle, the two pairs of the interlinked Us, are at a distance of about half a pole diameter - but that is difficult to achieve in practice, because the smaller the distance, the greater the danger a slight miscalculation ( of how much the wraps will slide on the surface of the pole before they start to grip it ) will lead in a prematurely "closed" hitch, when the distance would be zero, and the wraps would not yet be pre-tensioned as much as we would had wished. That is why one should better start from a position he anticipates that will lead in a distance of about one pole diameter, and then anything more he gains ( = any shorter umbilical cords he gets ), by pulling the end even more forcefully, will be a bonus - but following this conservative tactic he will not run the danger to be left with a closed, locked, but still not very tight hitch ! Because, and that is a good point to re-state it again, when this hitch is pre-tensioned, and it is locked, it remains locked for ever ! No way one can untie it - I had left the end of the Tail like this on purpose, because that is how it will look, when you apply the only trick you can do to untie such a tight, permanent knot : you cut it... Meaning that if you had tied it in the middle / in-the-bight of a rope, now you have not only untied it, but you have also made the one rope two !

( I had cut the rope just where it exits the slipped overhand knot - which slipped overhand knot can not be un-slipped, of course -, and then I had inserted a stick into its bight, and using it as a level, I had pulled the cut end off its casting. When one does this, the nub of the overhand knot is loosened a little bid, and then he can untie the whole hitch easily ).

Loose - because the knot you see is set up, but it is not tight. Its segments follow the path they would had followed if/when they were/are tensioned ( and I did that just to show the knot as it would look in its final stage, when it is tensioned, i.e., when the two parts of the yoke have approached each other at the "front" side of the pole, not in its initial stage, when they are close but still at the "rear" side of the pole, as in the pictures of the previous post ). Really tensioned / tight Yoke hitches are those shown in the first post, and in the thread about the tackled hitches.

Why, on Earth, do the Tackled hitches work, against all odds ? I am proud to ask this question, and I am more proud to answer : I do not know. What is the most precious achievement of the human civilization that should be maintained, at all costs, is its orientation towards the unknown. We have two wraps, which are dragged, by their crossing points, towards each other - so one would expect that they will slide, they will rotate ( =revolve around the axis of the pole ), and, eventually, those crossing points will 'kiss" each other, and any motion of the parts of the mechanism ( the two parts of the yoke, the two interlinked Us ) would come to a halt. Yet, this does not happen. By pulling the end(s), and reducing the amount of rope length from the hitch, two things happen, simultaneously : First, the wraps shrink, the length of their circumference is decreased. Second, the wraps slide, they rotate, the two umbilical cords in between them are shortened, and their crossing points approach each other. It seems that, at some point for unknown to us reasons, those two things change gear, but they put a different one : the one starts to happen more intensely than the other, and once the previous equilibrium ( where both were happening at the same pace ) is "broken", there is no turn back. From now on the wraps shrink faster than they slide, and their shrinkage prevents them from sliding as fast/much as they did, and, at some point, it makes them be "glued" onto the surface of the pole - and then they can not slide and rotate any more : any subsequent pulling of the end(s), the only thing it can do, is to make them shrink more, not to make them slide and rotate - not even a mm ! The future generations of honest knot tyers, who will not be as scientifically illiterate, as arrogant, as immersed in ego-trips, most of the times just pretending and showing up in front of an imaginary / non-existing audience, as WE are, will understand the mechanism. They will use laboratories, instruments, numbers and statistics, they will follow the centuries old and still/always young scientific method, they will create mental images and models of the mechanisms involved, and they will explain the phenomenon. Although the future is not ours to see, it will be, and since it will be, those things will happen, that is for sure.

Right from the first post where I had described what a "tight hitch" is, I had also emphasized that it is also a self-locking binder - in fact, I could nt find something fundamental that could serve to distinguish them, other than the mere presence of the hitched object, of course ( which, sometimes, by the "push" the surface of the object applies on the nub, it changes its geometry and enhances its nipping / gripping power, relatively to the power of the same nub used for the corresponding binder, and suspended in mid-air ). Now, a binder which utilizes a mechanical advantage can be considered as a rope-made, block-and-tackle simple machine, a system of "soft" pulleys , if you like. The Poldo tackle is another such system - but also all the "tight hitches" I had tied ( the TackleClamp hitch and the Locked Double Cow hitch included ) can serve such a purpose.

Actually, I first form the loose knot in-hand ( and in the middle of the line, because I always like to tie it as a TIB hitch, although it is not required ), then I insert it on the pole, and I tie the ( slipped ) overhand knot only at the very end. However, you may find an easier and quicker way - or a "simpler" one, because personally I feel obliged to follow "transparent" (= not "magical" ) tying methods, in which the average knot tyer can watch the gradual transformation of the shape of the knot easily, and even, if possible, tying methods in which the shape of the knot does not change much, from start to finish. This may make those tying method more easily understandable, but not necessarily easier or quicker !

The two parts of this hitch, which are forcefully connected to each other, while they approach each other during pre-tensioning, seemed to me to justify this name. In Germanic languages, like English, the etymology is the same. I copy, from Wikipedia :

I use the ( not very scientific ) method shown in the pictures to get an idea of how much the hitch will "close" ( = how much the two parts of the yoke, the two crossing points of the interlinked opposed Us, will approach each other ), under loading, by pulling the end against the pole at all times. Details : After the initial removal of the slack, I do not intervene on the hitch any more - I only keep loading the end. I mark the pole with parallel lines ( every 60 degrees - although, to get a greater accuracy, sometimes I use denser lines, every 30 degrees ). I weight the water I pour into the bucket(s) with a cuisine balance/scales. Finally, when I step on the eye of the overhand loop, I pay some attention to my own balance, because I do not know how acrobats do it : how they manage to fall into the bucket with the water, without being hurt...

The hitch shown in the previous post, after its pre-tensioning with 100 kg. We see that the hitch has "closed" when the two crossing point have been dragged by their umbilical cords and had reached two diametrically place points on the surface of the pole. Their optimum distance should be about 1 pole diameter, i.e., at about half of the distance they are now - so , at the initial setting of the hitch ( with this particular pole, rope and pre-tensioning weight ), one should had started from a configuration where the two parts of the yoke were at about half a pole diameter apart, and not in contact to each other. Of course, with lighter pre-tensioning weights/loads, this initial distance should be even bigger, because otherwise, under a lighter loading, the two parts will not be able to come as close to each other as we would had wished. I had shown an initial stage of this hitch with the two parts "kissing" each other, just to simplify the mental image of the loose knot. In fact, I always start pulling the end of the Yoke hitch, where I had removed all slack, when the two parts of the yoke are already at about half pole diameter, or even more ( at 90 degrees ), and my knots, with similar ropes, poles and pre-tensioning loadings, do not close prematurely. It is a matter of experience : after some time, one becomes able to guess where his hitch will lock, and if, during the pre-tensioning, he understands that it will lock too early or too late, he can always stop, loosen the hitch, return to a more proper initial stage, and start again - because, as I had emphasized, if/when this hitch is closed and locked, it becomes rock solid, and untiable - then, there is no turn back !

The "top","front", "main" side of this hitch. We see the two umbilical cords, which could /better had half the length they have now - which means that the knot should had started to shrink, by the pulling of its end, from a more "loose" initial configuration of its segments. As I said in a previous post, the distance between the two parts of the yoke before the start of the pulling, which was zero in the case of the shown knot, could had been one half pole diameter, or even 90 degrees. [ All this tying and trying of the tight "Tackled hitches" ( not only those which I had presented in those two threads, of course, but also of dozens of others, which I thought they are less interesting ...), was not without some cost for me : I now suffer from severe back pains, and so I can not continue ( although I wish it very much...) and "finish" this exploratory journey at this unchartered area of the KnotLand. I can not even tie and try other knots, for the attachment of the Tail End within the tip of the bight/U of the second wrap, some of which I have in mind... The interested reader may find a better solution than the slipped overhand knot I had used, which would retain the TIB-ness of the hitch, while it could be untiable more easily after hard loading. Notice that the "over"/"under" relation of the continuation of the Standing End and the bight/U of the first wrap does matter : this knot is not symmetric. In the one case it is topologically equivalent to the unknot, and in the other to the overhand knot - and this offers some flexibility in the choice of the knot between the Tail End and the tip of the second bight/U. ] For the moment ( I hope...), that s all, folks !

You should find something that leads to the "loose"(=not-yet-tensioned ) knot, before the start of the pulling of the end, shown in the pictures of Reply#1 and Reply#3, not to the "closed", already pre-tensioned knot.